Hydrocarbon conversion process



April 8, 1947- c. w. WATSON HYDROCARBON CONVERSION PROCESS Filed Aug.18, 1944 Sn 2o @165mm NNM lull

Patented Apr. 8, 1947 HYDROCARBON CONVERSION PROCESS Claude W. Watson,Scarsdale, N. Y., assigner to The Texas Company, New York 17, N. Y., a.corporation of Delaware Application August 18, 1944, Serial No. 550,101

3 Claims.

This invention relates to the manufacture of gasoline to producegasoline of improved quality from naphtha hydrocarbons.

The presentapplication isa continuation-inpart of Serial No. 500,599,filed August 31, 1943, for Hydrocarbon conversion process, and which isnow Patent No. 2,400,795, dated May 21, 1946.v

The invention has to do with the catalytic conversion of cracked andstraight run naphtha, or fractions thereof, into gasoline of increasedparailin and aromatic content and of improved octane value. It involvesa continuous method for effecting dehydrcgenation of straight runnaphtha andV hydrogenation of cracked naphtha in a common reaction zone.

The invention provides a method for the conversion of olefinic petroleumhydrocarbons of motor fuel range into motor fuel components of lowpotential gum content, high anti-knock value and excellent leadsusceptibility, especially suited for use in aviation fuels or othermotor fuels for high compression engines. It provides a process for theproduction of motor fuel of aviation grade from a relatively unsaturatedcracked naphtha and a relatively saturated naphthenic hydrocarbonfraction.

AsV disclosed in Patent No. 2,400,795, liquid olefinic hydrocarbons aresubjected to catalytic isomerization and the resulting isomerizate isreacted, under hydrogen transfer conditions, with cyclic hydrocarbonscontaining alicyclic methylene groups. The hydrogen transfer reactioneffects hydrcgenation of the olefins and dehydrogenation of the cyclichydrocarbons. By this combination of reactions, a petroleum hydrocarbonfraction of high olen content, such as a catalytically cracked naphtha,may be converted to a parainic blending stock of high anti-knock value.If a naphthenic fraction of motor fuel range is employed in the hydrogentransfer reaction with the cracked naphtha isomerizate, the naphthenesare dehydrogenated, and the resulting aromatic hydrocarbons furtherimprove the anti-knock characteristics of the reaction product. By thismeans it is possible to obtain a product having an octane number atleast as high as that of the original cracked naphtha, and usuallysubstantially higher than that of the cracked naphtha, and also havingalow bromine number and ability to meet the most stringent specicationsas to accelerated gum formation.

Also, as disclosed in Patent No. 2,400,795, the isomerized olens arereacted with hydroaroniatic hydrocarbon constituents of straight runnaphtha by contact with a solid hydrogenation-dehydrogenation catalystof the oxide or sulfide type at temperatures ranging from 750 to 950 F.and under pressures ranging from 50 to 1500 pounds per square inch.Also, as described in the parent application, straight run naphthahydrocarbons heated to the desired temperature are passed through areaction tower packed with the hydrogenation-dehydrogenation catalyst,while thel cracked naphtha hydrocarbons following :lsomeri. zation areintroduced to the tower at a plurality of succeeding points intermediatethe inlet and the outlet of the reaction tower.

The present application is concerned particularly with the procedureemployed in carrying out the combined dehydrogenation and hydrogenationreactions so as to effect transfer of hydrogen from hydroaromaticconstituents of the straight run naphtha to unsaturated constituents ofthe cracked naphtha.

More specifically, the invention of the present application involvesmaintaining a reaction tower or other elongated reaction zone packedwith the hydrogen transfer catalyst in solid granular form.Dehydrogenation of naphthene hydrocarbons is effected in one region,while hydrogenation of olenic hydrocarbons is effected in another regionof the reaction zone.

The procedure thus involves passing the straight run hydrocarbonsthrough a dehydrogenating section of the reaction zone at a temperaturein the range about 840 to 900 F. and preferably at about 850 to 860 F.The products of dehydrogenation then pass through a hydrogenatingsection wherein they are brought into contact with the cracked naphthahydrocarbons at a temperature in the range about 600 to 800 F. andpreferably at a temperature about 650 to 700 F. Advantageously, thecracked naphtha hydrocarbons are introduced directly to thehydrogenating section at a plurality of succeeding points in thedirection of straight run hydrocarbon iiow therethrough. Thetemperatures and proportions of the successive streams of crackedhydrocarbons are correlated so as to maintain the desired temperaturewithin the hydrogenating section, which temperature should not exceed amaximum of about 800 F.

The hydrogenating reaction is of exothermic character and thereforesucceeding streams of cracked naphtha may be introduced at progressivelylower temperatures, or in different proportions at substantially thesame temperature, in order to control the over-al1 temperatureprevailing within the hydrogenating section..

Free hydrogen is maintained present in both sections of the reactionzone in excess of 'that required for completely hydrogenating theolefinic 3 or other unsaturated constituents of the cracked naphtha feedand also in excess of that required for hydrogenating any sulfuravailable from the naphtha feed for reaction with hydrogen to vformhydrogen sulfide.

' Free hydrogen is produced in the dehydrogenating section whereinnaphthenic hydrocarbons are converted to aromatic hydrocarbons withlib'- eratlon of hydrogen. Provision may be made for recycling hydrogen,through the reaction tower.

Advantageously, hydrogen gas is separated from the products of theprocess and recycled to the dehydrogenating section of the reactionzone. The recycled gas can be heated to temperatures suiciently elevatedto provide the heat required in effecting the endcthermicdehydrogenation reaction..

The ratio of cyclic hydrocarbons to olefins for 'the hydrogen transferreaction will depend upon the degree of unsaturation of the oleiiniccharge stock and the available hydrogen in the cyclic hydrocarbons. Itis desirable to employ an excess of the cyclic hydrocarbons over thattheoretically required to supply all of the hydrogen necessary forsaturation of olens and for hydrogenation of available sulfur. Ratios ofcyclic hydrocarbons to olens in the charge may suitably range from 1.1to 1.5 times the theoretical ratio.

The process of the invention is especially adapted for the treatment ofolelnie' hydrocar.- bon mixtures such as cracked petroleum fractionsincluding naphtha hydrocarbons derived from either thermal cracking orcatalytic cracking. The relatively lower boiling portion. namely,boiling in the range below about 250 or below 300 F., of catalyticallycracked naphtha, is particularly suitable since it contains a relativelyhigh proportion of branched chain olefin hydrocarbons. While mention ismade of oleilnic naphtha obtained from cracking ,of petroleum,nevertheless it is contemplated that the olenic naphtha mentionedcycloparaifins, cyclooleiins, terpenes/ and polycyclic hydrocarbons ofalicyclic or mixed alicyclic-aromatic character. The hydroaromatichydrocarbons are preferred as hydrogen donors for the hydrogenation ofthe oleiins since they are dehydrogenated to aromatics. Naphthenichydrocarbons, consisting essentially of cyclohexane and its derivatives,boiling at a temperature not higher than the end boiling point of thedesired gasoline product, are especially desirable.

Straight-run naphtha such as derived from naphthene base crudes may beused as the source of the naphthene hydrocarbons required in the processas hydrogen donors. It is preferred to use a naphthene stock high in Csring naphthene hydrocarbons boiling within the range of aviationgasoline, that is, boiling in the range below 250 or 300 F. A naphthenicgasoline having a C. F. R. M. octane number of 60 to 70 or in excess of55 is preferred. v

In order to describe the invention in more detail, reference will now bemade to the accompanying drawing illustrating a method of flow suitablefor carrying out the hydrogen transfer reaction irrespective of whetheror not the olelnic feed stock has been subjected previously toisomerization.

The numeral I designates a vertical reaction tower packed with aplurality of beds of catalyst 2, each bed being supported by aperforated tray 3. The catalyst may be of the molybdena-alumina type inwhich the oxides of molybdenum amount to about 9% by weight of thecatalyst.

Straight run naphtha from a source not shown is conducted through a pipe4 and a. heater 5 wherein it is heated to a temperature of at least 850F. .and not in excess of about 925 F. The heated naphtha passes througha pipe 8 to the top of the reaction tower I. The straight run naphtha,advantageously boiling` in the range -about to 300 F., enters the top ofthe tower in vapor phase and ows downwardly through the catalyst beds inseries. y Recycled gas, from a source which will be referred to later,is heated in the heater 8 to a temperature which may range as high as`1200 F. or to a temperature sumciently high to provide the heat ofreaction required for effecting dehydrcgenation of straight run naphtha.The heated gas is passed through pipe 8 which communicates with branchpipes I0, II and I2. These branch pipes extend into the upper portion ofthe tower I, in which portion dehydrogenation is effected.' The heatedgases are thus introduced at a .plurality of succeeding points and theproportions and temperatures of the several entering gas streams arecorrelated so as to maintain substantially the same temperaturethroughout the' catalyst mass in the dehydrogenating section of thetower.

It is advantageous to avoid a substantial temperature drop in thissection of the tower. It is preferred to maintain a uniform temperaturewithin the range about 840 to 870 F.

Higher temperatures are avoided so as to prevent hydrocarbon cracking orother undesirable reactions. On the other hand, at temperatures below840 F. the dehydrogenation reaction is relatively slow. At a temperatureof about 850 to 860 F. the reaction is about 90% completed provided theproper time of contact is realized.

The time of contact is dependent upon space velocity, which in turn is`maintained within the range about 0.1 to 0.5 volume of straight runnaphtha measured as liquid at 60 F. per volume of catalyst per hour.

The pressure maintained within the reaction tower ranges from about 400to 800 pounds and preferably about 700 pounds.

As indicated in the drawing, the dehydrogenating reaction issubstantially completed during passage of the hydrocarbons through therst bed of catalyst or section of the tower. The products ofdehydrogenation then pass on through the succeeding catalyst bed or bedscomprisingv the hydrogenating section.

Cracked naphtha, boiling in the range up to about 300 F., is conductedfrom a source not shown through a pipe I5, whichv in turn communicateswith branch pipes I6 and I1. These branch pipes may lead to separateheaters or heat exchangers I8 and I9 respectively, wherein the naphthastreams are heated t0 the desired temperature or temperatures.

The portion of the cracked naphtha, passing from the heater I8 throughpipe 20, may enter the reactor I at comparatively -low temperatures, forexample at a. range from 100 to 200 or 300 F. It is thus used to reducethe temperature of the products of dehydrogenation passing to thehydrogen section of the tower. If desired, the cracked naphthahydrocarbons may enter through pipe 20 in liquid phase so that theirchiasso.'

heat of vaporization is utilized'within the reaction tower to cool theproducts of dehydrogenation to a temperature of about 700 F. or to a,temperature below about 800 F. The cracked'naphtha and thedehydrogenated naphtha, together with free hydrogen, ow in the presence.of each other through the hydrogenating sections of the tower, so thathydrogenation oi' the unsaturated constituents of the cracked naphthaoccurs.

Since the hydrogenating reaction is expthermic, it is advantageous toemploy split feed of the cracked naphtha. Therefore a succeeding streamis introduced from -the exchanger I9 through pipe 2l. The proportions ofcracked naphtha entering at each succeeding point, the spatialdistribution of the several streams, and the temperature at which eachstream enters are correlated so as to maintain a temperature about 650to '700 F. within the hydrogenating section. As previously indicated,each stream may enter at substantially the same temperature, control ofreaction temperature being effected by adjusting the relativeproportions of the streams.

The straight run naphtha introduced to the top of the tower may rangefrom about 35% to '75% by volume of the combined straight run andcracked naphtha feed. i

The products of reaction are continuously 1 drawn off from the bottom ofthe reactor through a pipe 30 to the lower portion of the fractionator3l. The fractionation is carried out so as to remove a distillatefraction containing gasoline hydrocarbons boiling up to about 300 to 320F.

The distillate is removedr through a pipe 32 and condenser 33 to areceiver 34. The condensate collects therein and is continuously drawnoff through a pipe 35.

The gas is vented oi through a pipe -36 from which it may be discharged,at least in part, through pipe 31. n

Since it is usually desirable to carry on the process with hydrogenrecycle, provision is made for conducting the gas from the pipe 36through the pipe 38 leading to the heater 8, previously mentioned andwherein the recycle gas is heated prior to return to the reaction tower.The amount of gas recycled usually ranges from about 5,000 to 10,000cubic feet per barrel of straight run or donor feed, the gas beingmeasured under standard conditions.

When the gas contains a relatively large amount of hydrogen sulfide,provision may be made for scrubbing it prior to recycling. In such case,the gas is passed through pipe 40 into a scrubber 4|, wherein it isscrubbed with soda ash solution or other scrubbing medium to effectremoval of hydrogen sulfide. The resulting scrubbed gas is then returnedthrough pipe 42 which communicates with pipe 38. Since the bulk of thehydrogen sulfide is removed from the system in the condensate leavingthe receiver 34, such scrubbing is usually unnecessary.

In carrying out the process it will be apparent, from the foregoing,that the space velocity in the hydrogenating section of the tower isrelatively greater than that prevailing in the dehydrogenating section.In the dehydrogenating section, the space velocity does not exeed 0.5,while in the hydrogenating section it will range from about 1 to 3 andis preferably maintained at about 2 liquid volumes of combined naphtha(exclusive of gas) per volume of catalyst per hour.

The procedure described is particularly advantageous for the treatmentof naphtha, contain- V catalyst used in this process, particularly atthe temperatures most effective for carrying out dehydrogenation. It istherefore important to maintain a high partial pressure of hydrogenpresent* in order to keep the catalyst free from sulfur. The availablesulfur reacts with free hydrogen to produce hydrogen sulfide whichv isdischarged from the system. The present process therefore permitsmaintaining a large amount of 'hydrogen present in the dehydrogenatingsection so as to prevent catalyst degradation due to the sulfurcontained in the feed naphtha.

It is for this reason that the olefinic feed is not introduced with thestraight run naphtha. Instead, it is not introduced until a point in thepath of travel of the straight run hydrocarbons through the reactionzone is reached where the dehydrogenating reaction is substantiallyentirely completed. The reduction in the amount of hydrogen present,which would occur as a result of having olens present in thedehydrogenating section is thus avoided.

The hydrogenating reaction is effected, in accordance`with the presentinvention, at a lower range of temperature, such that the sulfur hasrelatively low affinity for the catalyst. The process thus provides ameans for effecting desulfurization as well as hydrocarbon conversion..It is useful for effecting both desulfurization and hydrogenation ofcracked naphtha.

It is contemplated that with straight run feed stocks containing llessthan .01% sulfur, the process may be operated without substantialhydrogen recycle. On the other hand, with straight run feed stockscontaining sulfur in excess of .05% by weight, provision may be made fordesulfurizing the straight run naphtha prior to the hydrogen transfertreatment. In this ease, the straight run naphtha hydrocarbons of highsulfur content may be subjected to the action of a catalyst of thefullers earth or bauxite type, at a temperature in the range 650 to 900F., to effect desulfurization. The desulfurized naphtha from which thesulfur has been removed is then passed to the hydrogen transferreaction.

It is contemplated carrying out the hydrogen transfer reaction processso that no hydrocarbon cracking occurs as evidenced by the obtaining ofa liquid hydrocarbon recovery of at least 98% by weight and preferablyat least 99% of the liquid feed hydrocarbons. The C4 hydrocarbon, andlighter gas fraction of the eiuent stream of reaction products, consistsessentially of hydrogen. In other words, the hydrogen is in excess ofand is usually not less than 97% by weight of this fraction.

'I'his is in contrast with the conventional hyy ananas merization ofoieilns with subsequent cracking of products formed by polymerization;cyclization of .parai1ins,` lcondensation of aromaticsw; etc. Thesel.destructive conversion reactions are. so pronouneed that in theconventional operation, even with a, large amount of hydrogen gasrecycle, the

catalyst is'rapidly fouled so that regeneration is necessary after to1.2 hourson stream.

The hydrogen' transfer catalyst used in the process of this inventionadvantageously comprises a mixture` of aluminum oxide in any of itsvarious forms with from 1 to 50 Weight per cent naphthenic hydrocarbonsin the `presence of the hydrogenation-dehydrogenation vcatalystnevertheless it is also contemplated that the' process mayhave`application tothe treatment of unsaturated hydrocarbons derivedfrom other sources and also to the treatment of other unsaturatedmaterials such as contained in fatty oils and fatty acids or derivativesthereof obtained from vegetable, animal. or fish oil sources. Thustheprocess may be used for effecting saturation of these unsaturatedfatty oil or fatty acid substances by reaction with naphthenic hydrocar-A bons derived from straight-run naphtha.

of an oxide or sulde of a metal selected from reaction zone correspondsto a space velocity of about .5, while the flow through thehydrogenating section corresponds to a space velocity of about 2.

The operation is carried out with a gas recycle rate of about 8,000cubic feet per barrel of combined naphtha feed so as to maintain ahydrogen partial pressure in the eiiluent product stream from'thereaction of about 400 to 700 pounds per square inch gauge.

The liquid product obtained, after a minimum of 100 hours continuousflow without interrup tion for catalyst reactivation, amountsto about98.7% by weight of the combinednaptha feed. The following tabulationsets forth the characteristics vof the feed naphtha fractions and theresulting product, including those of a blend of the feed naphthas inthe proportion as actually charged, namely 35% cracked naphtha to 65% ofstraight run naphtha by weight.

StraightRun Cracked Blend Product Gravity API 57. 4 67. 7 62. 3 62. 5 Bur, Wt. .01 Bromine No 0.6 105 35 1 Distillation:

I. Biolly. 168 er E. P l300 Aromatics, Wt 85. 4 Octanes:

AFD-IC C1ear Below 71.2 72.4 AFD1C+4cc- TEL. 88. 82. 0 85 87. 3

catalyst such as aluminum chloride-hydrocarbon complex.

While mention has been made of reacting olefinie hydrocarbons derivedfrom petroleum with Obviously many modicationsand variations of theinvention, as hereinbefore setaforth, may be made without departing fromthe spirit and scope thereof, and therefore only such limitations shouldbe imposed as are indicated in the ap pended claims. l

- I claim:

l. A continuous method of preparing gasoline rich Ain aromatichydrocarbons and saturated aliphatic hydrocarbons from straight run andcracked naphtha hydrocarbons boiling within the range about to 300 F.and containing sulfurbearing compounds in substantial amount involv..

1 ing dehydrogenation of hydro-aromatic constituents of straight runnaphtha and hydrogenation of oleiinic constituents of cracked naphthawhich comprises maintaining an elongated reaction zone containing Yasubstantially stationary mass of hydrogenation-dehydrogenation catalystand through which straight run hydrocarbons undergoing treatment flowfrom the inlet through a.

dehydrogenating section and thereafter through a hydrogenating sectionto the outlet of the reaction zone, continuously introducing a stream ofstraight run hydrocarbons vto said inlet, effecting contact betweenintroduced hydrocarbons and catalyst in the dehydrogenating section atan elevated temperature of about 850 to 860 F., under a pressure withinthe range about 400 to 800 pounds and with a space velocity in the rangeabout 0.1 to 0.5 liquid volumes of naphtha per hour per catalyst, and inthe absence of oleflnic constituents of the cracked naphtha hydrocarbonssuch that dehydrogenation of said hydroaromatic constituentsoccurs withliberation of hydrogen in substantial amount, continuously introducingto the hydrogenating section of the reaction zone cracked hydrocarbons,causing the products of dehydrogenation and the introduced crackedhydrocarbons to iiow concurrently and in direct contact through thehydrogenating section at an elevated temperature in the range about 650to 700 F. and with a space velocity in the range about 1 to 3 liquidvolumes of combined naphtha per hour per catalyst such thathydrogenation of cracked hydrocarbons with said liberated hydrogenoccurs, correlating the proportion of straight run hydrocarbons tocracked hydrocarbons charged so that the cyclic hydrocarbons are presentin an amount equal to about 1.1 to 1.5 times the molecular equivalent ofthe olens and such that free hydrogen in substantial amount ismaintained in the reaction zone, continuing the flow of hydrocarbonsthrough the reaction zone for substantially in excess of 100 hourswithout catalyst regeneration, continuously discharging from the outlethydrocarbon products of reaction and free hydrogen, the liquidhydrocarbons contained in said products amounting to at least about 98weight per cent of the combined naphtha feed and the C4 hydrocarbon andlighter constituents of said products consisting of not 9 less thanabout 97 weight per c'ent hydrogen separating hydrogen gas from thedischarged products, heating the separated gas and introducing theheated gas at a plurality of succeeding points in the dehydrogenatingsection of the reaction zone to thereby maintain substantially uniformtemperature throughout said section.

2. A continuous method of preparing gasoline rich in aromatichydrocarbons and saturated aliphatic hydrocarbons from straight run andcracked naphtha hydrocarbons boiling Within the range about 100 to 300F. and containing sulfur bearing compounds in substantial amountinvolving dehydrogenation of hydro-aromatic constituents of straight runnaphtha and hydrogenation -of olenic constituents of cracked naphthawhich comprises maintaining an elongated reaction zone containing asubstantially stationary mass of hydrogenation-dehydrogenation catalystand through which straight run hydrocarbons undergoing treatment flowfrom the inlet through a dehydrogenation section and thereafter througha hydrogenating section to the outlet of the reaction zone, continuouslyintroducing a stream of naphthene straight run gasoline having a C. F.R. M. octane number of substantially in excess of 55 to said inlet,effecting contact between introduced hydrocarbons and catalyst in thedehydrogenating section at an elevated temperature of about 850 to 860F., under a pressure within the range about 400 to 800 pounds and with aspace velocity inthe range about 0.1 to 0.5 liquid volumes of. naphthaper hour per catalyst and in the absence of oleflm'c constituents of thecracked naphtha hydrocarbons such that dehydrogenation of saidhydro-aromatic constituents occurs with liberation of hydrogen insubstantial amount, continuously introducing to the hydrogenatingsection of the reaction zone cracked hydrocarbons, causing the productsof dehydrogenation and the introduced cracked hydrocarbons to nowconcurrently and in direct contact through the hydrogenating section atan elevated temperature in the range about 650 to 700 F. and with aspace velocity in the range about 1 to 3 liquid volumes of combinednaphtha per hour per catalyst such that hydrogenation of run naphtha andhydrogenation of olenic coni y stituents of cracked naphthawhichcomprises maintaining an elongated reaction zone 'contain-v ing a massof hydrogenation-dehydrogenation catalyst and through'which straight runhydrocarbons undergoing treatment flow from .the inlet through 'adehydrogenating section and thereafter through a hydrogenating sectionto the outlet of the reaction zone, continuously 'introducing a streamof straight run hydrocarbons to said inlet, effecting contact betweenintroduced hydrocarbons and catalyst in the dehydrogenating section atan elevated temperature of about 840 to 870 F., `under a pressure withinthe range about 400 to 800 pounds and with a space velocity in the rangeabout 0.1 to 0.5 liquid volumes ofnaphtha per volume of catalyst perhour, and in the absence of olenic constituents of the cracked naphthahydrocarbons such that dehydrogenation of said hydro-aromaticconstituents occurs with liberation of hydrogen in substantial amount,

continuously introducing to the hydrogenating cracked hydrocarbons withsaid liberated hydroent in an amount equal to about 1.1 to 1.5 times themolecular equivalent of the olens and such that free hydrogen insubstantial amount is maintained in the reaction zone, continuing theiiow Aof hydrocarbons through the reaction zone for substantially inexcess of 100 hourswithout cata lyst regeneration, continuouslydischarging from the outlet hydrocarbon products of reaction and freehydrogen, .the liquid hydrocarbons contained in said products amountingto at least about 98 Weight per cent of the combined naphtha feed andthe C4 hydrocarbon and lighter constituents of said products consistingof not less than about 97 weight per cent hydrogen, separating hydrogengas from the discharged products, heating the separated gas andintroducing the heated gas at a plurality of succeeding points in thedehydrogenating section of the reaction zone to thereby maintainsubstantially uniform temperature throughout said section.

3. A continuous method of preparing gasoline rich in aromatichydrocarbons and saturated aliphatic hydrocarbons from straight run andcracked naphtha hydrocarbons boiling Within the section of the reactionzone cracked hydrocarbons, causing .the products of dehydrogenation andthe introduced cracked hydrocarbons to now concurrently and in directcontact through the hydrogenating section at an elevated temperature notin excess of about 800 F. and with a space velocity in the range about 1to 3 liquid volumes of combined naphtha per volume of catalyst per hoursuch that hydrogenation of cracked hydrocarbons with said liberatedhydrogen occurs, correlating the proportion of straight run hydrocarbonsto cracked vhydrocarbons charged to the reaction zone so that the cyclichydrocarbons are about 1.1 to`1.5 times the molecular equivalent oi theolefins and such that free hydrogen in substantial amount is maintainedin the reaction zone. continuing the now of hydrocarbons through thereaction zone for substantially in excess of hours without catalystregeneration, continuously discharging from the outlet hydrocarbonproducts of reaction and free hydrogen, the liquid hydrocarbonscontained in said products amounting to at least 98 weight per cent ofthe combined naphtha feed and the C4 hydrocarbon and lighterconstituents of said product consisting of not less than about 97 weightper cent hydrogen, separating gas from the discharged products, heatingsaid gas and introducing the heated gas at a plurality of succeedingpoints in the dehydrogenating section of said reaction zone to therebyImaintain substantially uniform temperature throughout said section.

CLAUDE W.y WATSON.

REFERENCES CITED The following references are of record in the lle ofthis patent:

UNITED STATES PATENTS Number Name Date 2,241,393 Danner ..-Ma-y 13, 19412,303,075 Frey Nov. 24, 1942 2,283,854 Friedman May 19, 1942` 2,293,759Penisten Aug. 25, 1942 2,289,716 Marschner July 14, 1942 2,335,684 MayerNov. 30, 1943 2,341,269 Day Feb. 8, 1944 2,367,530 Ruthrui Jan. 16, 1945OTHER REFERENCES Egioff et a1. pubucaun 1n the on and Gas Journal, May21, 1931, pages 40 and 155.

